Simple Unit Testing Environment

unit_tester_annotated.py

# performs a single unit test 
# accepts a function to test, a test case input and its corresponding expected output
def unit_test(function_to_test, test_input, expected_output): 
    try: # try something (whatever is in the code block) 
      function_output = function_to_test(test_input)

    except Exception as error: # if it DOES NOT work then catch the error using the except keyword
    # Exception is a general "catch-all" exception
      # catch the Exception and store the error message as a variable called error
        print("Error occurred with test input: [{0}] value: {1}\nError Message: {2}\nCorrect the error and try again.\n"
        .format(type(test_input), test_input, error)) # use a template (format) string to output useful information

    else: # if it works move to the else statement block (scope is preserved from the try block)
      try: # try confirming that the function's output matches the expected output using the assert keyword
          assert function_output == expected_output
          print(unit_test_response(True, test_input, function_output, expected_output)) # True is the first argument signifying the test passed
      except AssertionError: # in this case the exception (error) that is caught is AssertionError meaning the function's output DID NOT match the expected
          print(unit_test_response(False, test_input, function_output, expected_output)) # False is the first argument signifying the test failed
    
def unit_test_response(correct, test_input, function_output, expected_output): # generates the message output from the completed test (used on lines 16 / 18)
    score = "Test Passed" if correct else "Test Failed" # ternary statement determines whether to label the test as Pass or Fail
    return "{0}\nInput: {1}\nExpected Output: {2}\nFunction Output: {3}\n".format(score, test_input, expected_output, function_output)

def run_unit_tests(function_to_test, test_list): # iterates through a list of test case pairs (called tuples in Python)  
    for test_tuple in test_list:
        test_input, expected_output = test_tuple # "unpacks" (Python terminology) the tuple into the two variables
        # test_input = test_tuple[0] # (can be written this way as well which may look more familiar)
        # expected_output = test_tuple[1] 
        unit_test(function_to_test, test_input, expected_output) # calls the unit_test function for each iteration of the loop


"""
Process Flow:
1) iterate (loop) through the list of test cases
2) store the test input and its corresponding expected output via unpacking of the current test case tuple (that sounded way more scifi that it needed to)
3) for each iteration of the loop call the unit_test function passing in the current test input and expected output
4) follow the try / except path
5) call the unit_test_response function to create the message output
6) repeat until out of test cases
"""

# Uncomment below to try it out using the is_leap function as an example
  # try putting in wrong values or even incorrect types (such as a string) and see what happens
  # you can use this with codelens or put in print statements throughout the functions to better understand the system
# test_list = [(1900, False), (1956, True), (1600, True)] # each element in this list is a tuple designated by the ()

# def is_leap(year):
  # return year % 400 == 0 if year % 100 == 0 else year % 4 == 0

# run_unit_tests(is_leap, test_list)